Soundless double propeller for aeroplanes



May 18 1926. 1,585,218

G. WATANABE I SOUNDLESS DOUBLE PROPELLER FOR AEROPLANES Filed March 26, 1924 Patented Ma 18, 192s.

UNITED STATES GENNOJO WA'I'ANABE, 033 LOS ANGELES, CALIFORNIA.

SOUNDLESS DOUBLE IPRQPELLER FOR AEROPLANES.

Application filed March 26, 1924. Serial No. 702,063.

This invention relates to improvements in aeroplane propellers, and the principal object of the invention is to produce a propeller designed 'to be operated Without noise or sound.

Vith this object in view, I have provided a double propeller, consisting of two similar propellers mounted to rotate on the same axis, means for adjusting one of the propellers to and from the other propeller, and means for adjusting the last-named propeller whereby its blades are advanced in position relative to the first-named propeller.

The soundless operation of the propeller will be obtained only at a predetermined speed of rotation combined with a given velocity or speed of the aeroplane. This condition is attained when the speed of the aeroplane is such that the distance traveled through the air medium is approximately equal to half of the wave length produced by the rotation of the propeller, and the arrangement is such that the positionoccupied by the first propeller at one point in its rotation, will be subsequently occupied by the second propeller, thereby producing an interference with the sound waves generated by the first propeller. In'other terms, the two generated systems of sound waves, whose amplitude and. wave length are the same, and phase difi'erence is half the .wave length, are then in interference, resulting in soundless rotation of the propellers. The aeroplane must therefore travel a distance equal to half of the wave lengths produced by the rotationof the propellers.

With these ends in view I have provided v two complementary propellers and means for adjusting them, as hereinafter more fully described, and shown in the accompany drawings.

\ In the drawings, Figure 1 is a side view showing two propellers mounted on a shaft .in accordance with my invention. Fig. 2 is a fragmentary and detail view of the same,

showing the adjusting means forv the second or rear propeller.

Referring to the drawings, the driving shaft 3, has mounted at the forward end thereof, the advance or first propeller 4, se-

cured by a nut 5, and adapted to beclamped in any angle or position relative to theshaft- "3. A second or rear propeller 6, is adjuste ablelongitudinally r ative to shaft 3, and

' forced by a feathering key 7, to rotate synchronously relative to the shaft. The propeller 6 is clamped in any position relative to the first propeller 4, by means of clamp screws 8, of which there are two rows on opposite sides of the propeller, engaging with recesses 9, in the supportlng shaft.

From the foregoing description it may be seen that I have provided means for adjustment of two complementary propellers so that the sound waves produced by the rotation of the first propeller, will be in interference with the sound waves produced by the rotation of the second propeller.

It is to be understood that the result obtained is practically soundless, but in actual practice the result will not be perfectly soundless, owing to air currents and to the temperature difference due to height of the aeroplane in the air.

If, in use, the practically soundless result is not attained by the longitudinal adjustment of the second propeller along its axis, then the first propeller is adjusted so that its blades are at a different angle or advanced in rotative position, relative to the blades of the second propeller.

IVhile simple and eflicient means are provided for accomplishing the objects of the invention, and the elements shown and described are well adapted to serve the purpose forwhich the are intended, it is to be understood that do not limit myself to the precise construction shown and described in the drawings, but that minor changes and alterations may be resorted to sitioning them on said axis whereby the sound waves generated are in interference.

2. The method of neutralizing aeroplane propeller "sound waves, consisting of rotating two similar propellers on the same axis, and one in advance of the other, and in positioning them on said axis whereby the two generated systems of sound waves of equal amplitude and wave length will have a phase difference of half a wave length.

3. The method. of neutralizing aeroplane sound waves, consisting of rotating two similarpropellers on a common axis, and in relative positions whereby the sound waves Y generated by one propeller are in interference with the sound Waves generated by the other propeller.

4. The method of adjusting two complementary propellers on a common driven axis, consisting of positioning them longitudinally to and from one another, and in advancing the blades of one propeller in rotative position relative to the other propeller whereby the two generated systems of sound Waves are in interference.

5. The method of adjusting two complementary propellers on a common driving axis consisting of changing their longitudinal positions relative to one another and changing the angular advancement of the blades of one propeller relative to the blades of the other propeller whereby the Wave amplitude and length are equal, and the phase difference is equal to half a wave 20 length.

In testimony whereof, I hereunto affix my signature.

GENNOJO VVATANABE. 

